Arrangement for increasing the power of repeater circuits



Nov. 9, 1926.

1,605,972 H. NYQ-UIST ARRANGEMENT FOR INCREASING THE POWER OF'RErEATER-CIRCUITS Filed August 26, 1924 IVNTPR 5499268815 A TTORNE Y Patented Nov. 9, 1925.

HARRY NYQUIST. OF JACKSON HEIGHTS, NEVI YORK, ASSIG-NOR TO AMERICBl-T TELE- PHONE AND TELEGRAPH COMPANY, A CORPORATION F NEW' YORK.

ARRANGEMENT FOR INCREASING THE POWER OF REPEATER CIRCUITS.

Application filed August 26, 1924. Serial No. 734,341.

This invention relates to repeater circuits and more particularly to arrangements for increasing the output power of the amplifiers employed in repeater circuits.

in a repeater circuit of the 22 type it has been proposed to increase the output power of each amplifier.- by making the impedance of the load into which the amplifier works greater than the internal impedance of the amplifier. Vhere no filter is employed in the repeater circuit this may be readily accomplished without disturbing the passive impedance of the repeater as viewed from the line to which it is connected, by chang ing the ratio of transformation between the output circuit of the amplifier and the line to which it is connected, at the same time making a compensating change in the input impedance of the amplifier in the repeater path transmitting in the opposite direction. here, however, a filter is employed in the amplifier circuit, the problem of increasing the load impedance is complicated by the presence of the filter and it becomes necessary to treat the circuits in a somewhat different manner. It is one of the objects of the present invention to provide an arrangement for the solution of this problem which will enable the employment of filters in the amplifier circuit and at the same time will permit of maintaining the passive impedance of the repeater at any desired value.

@ther and further objects of the invention will be clear from the detailed description thereof when read in connection with the accompanying drawing, Figure 1 of which shows a simplified diagram of a portion of a 22 repeater circuit in which no filters are employed, F ig. 2 of which is a similar diagram showing a filter in the output circuit of the amplifier, and Fig. 3 of which is a simplified circuit diagram of a 22 repeater employing the arrangements of the present invention.

Referring to Fig. 1, L designates a transmission line associated by means of a hybrid coil with the input side of an amplifier Alt and with the output side of an amplifier AW, the line L being balanced by the usual network N in order that the two paths of the 22 repeater may be substantially conjugate. in suchcircuits the impedance Z looking into the line L, should be equal to the impedance Z looking into the balancing network N in order that the repeater will be properly balanced. In order to avoid reflection losses, the passive impedance Z,, looking from the line into the 22 repeater, should be equal to the impedance of the line Z Similarly, the impedance Z,, looking trom the balancing network towards the hybrid coil, should be equal to the impedance Z of the balancing network. It has been found that the passive impedance Z, will be equal to the impedance Z of the line if the internal impedance Z i of the output circuit of the tube AlV be made equal to the load impedance Z, and if the input impedance Z, of the amplifier AE be made equal to the impedance Z, looking into the hybrid coil.

In circuits such as shown in Fig. 1, the power in the output circuit of a tube such as iii V may be expressed as where I is the output current, R is the real part of Z, the internal impedance of the tube, and a, is the real part of Z, the load impedance. It is, of course, desirable that the circuit he so designed that the maximum power be consumed in the load, and the power thus consumed may be expressed as PR Fora given voltage the power consumed in the load will be a maximum when the internal impedance Z, of the tube is the conjugate of the load impedance Z,, provided there is nothing to limit the current. In the case 01": the vacuum tube, however, the current is limited by saturation and if we should increase the applied voltage the current I would not be further increased after reaching the saturation point. Therefore, in order to increase the power consumed by the load we may increase the load impedance Z, so that it becomes greater than the internal impedance Z, of the tube, at the same time increasing the voltage to keep the current at a maximum.

In .he of a simple circuit such as that shown in Fig. 1, the increase in the load impedance Z, may be readily provided for by changing the ratio of the primary to the secondary winding of the transformer 10 so as to step up the impedance of the line and artificial line as seen through the transformer. This will, of course, produce a change in the passive impedance Z, of the repeater but may be compensated for by correspondingly increasing the impedance Z or, in other words, increasing the impedance of the potentiometer 11 so as to bring all Z, a smooth curve.

the passive impedance of the repeater back to equality with the impedance Z, of the ine.

lVhere 'a filter such as F is provided in the output circuit of the amplifier as shown in Fig. 2 the problem is not so simple. The inrpedancedrequency characteristic of the filter F will not, in general, be a smooth curve but will be irregular and will only be smooth in case its characteristic impedance Z as viewed from the tube AlV is equal to the impedance Z of the tube. If we make the impedance looking into the filter larger than the tube impedance in order to increase the power, the impedance of the filter will be irregular and compensat ing irre ularities would necessarily have to be introduced in the in ut circuit of the tube A, in order to have t e passive impedance By the present invention the power is increased by making the irrmedance of the output circuit of the tube larger than the internal impedance of the tube, thus introducing irregularities in the filter impedance, but these irregularities are compensated for by introducing a filter element having compensating irregularities in the input circuit or the tube transmitting in theopposite direction. As a consequence, the passive impedance Z, will be a smooth curve by reason of the fact that the irregularities introduzed in the transmitting branch will be compensated for by irregularities introduced in the receiving branch. In order to understand how this result is obtained, a theoretical discussion will now be given. "It may readily be shown that the passive impedance Z, of a repeater such.

asthat shown in Fig. l, for example, equals For simplicity in computation, we will next make Z n ai The relation between the impedances then becomes or putting we have "for the relation between the impedances.

Expressed in words, relation 5 is that the passive impedance of the repeater will be perfect at all frequencies (that is, will be equal to the line impedance Z at all frequencies), provided that the admittance of the input of the repeater element multi plied by is equal to the impedance of the output divided by a; at all frequencies. This can readily be accomplished by providing in the input a network or filter so constructd as .to be. element for element, the counterpart of the network in the output, series impeda'nces in one case being made to correspond to bridged admittances in the other, series coils being made to correspond to bridged condensers, series condensers being made to correspond to shunt coils, and series resistances being made to correspond to bridged conductances. In particular, if the nctworl-z in the output circuit as shown at N in F 3 is a low pass filter terminating in mid-shunt sections, the corresponding network N, in the input will be another low pass filter lnivingthe Sdll'lG cut-oil frequency but terminating in mid-series sections. More specifically, if the characteristic impedance Z of the filter in the output is made equal to the impedance Z, of the line and network-as they appear from the filter, the impedance Z of the filter in the input will be equal to the impedance Z otthe line and network as v ewed from the tube. The above relation is hereinafter re ierred to as a reciprocal relation.

Heretofore the filter in either the out put circuit or the input circuit of the amplifier (where no attempt is made to inliu crease the power by increasing the load impedance) consists of two sections of a low pass filter. In accordance with the present invention, however, one section will be sutficient in the output because of the fact that there will be another section N (not shown) in the input of the same amplifier. The output section could be made up as illustrated of a series coil and two bridged condensers. The section in the input would then be made up of a bridged condenser and two series coils, making a total of three coils and three condensers per repeater element instead of two coils and three condensers, as shown in Fig. 2. In other words, the amount of equipment would only be increased by one coil, notwithstanding that the load power may be increased as desired by placing the two filter sections one in the input and one in the output as illustrated.

As has already been stated, if we provide a filter in the output only, its impedance will not be smooth unless its characteristic impedance as viewed fromthe tube is equal to the tube impedance. By splitting the filter, however, the impedance of the one section may be increased to increase the power consumed in the load and the irregularties thus introduced will be compensated for by corresponding irregularities of the filter section in the imput. It will be understood, of course, that the two filter sections will be so chosen as to have the same critical frequency.

It will be apparent that with this arrangement the passive impedance of the filter is correct not only in the range for which the iter transmits freely but for every frequency whatever. This is a matter of considerable importance as 1t improves the passive impedance of the repeater in the neighborhood of the cut-oil" frequency.

t will be obvious that the general principes herein disclosed may be embodied in many other organizations widely different cuit of the filter and the other in the out put circuit, said units comprising series and shunt elements, the elements of the two units being so related to each other that for each unit a series impedance in one will correspond to a bridged admittance in the other.

3. In a signaling system, an amplifier, a network associated therewith comprising two units, one unit being arranged in the input circuit of the amplifier and the other in the output circuit thereof, each of said units comprising series and shunt impedances, one

of which is an inductance and the outher of which is a capacity, the elements of the two units being so related to each other that the series coil of the one corresponds to a bridged condenser in the other.

l. In a signaling system, an amplifier, a filter associated therewith comprising two sections, one section being arranged in the input circuit of the amplifier and the other in the output circuit thereof, one of said sections terminating in mid-shunt and the other terminating in mid-series.

In a signaling circuit, an amplifier, a filter associated therewith, said filter comprising two sections, one arranged in the input circuit and the other in the outputcircuit of the amplifier, each filter comprising series and shunt impedances, one of which is an inductance and the other of which is a capacity, the impedance elements of the two sections being so related to each other that a series inductance in the one corre sponds to the bridged condenser in the other, one of said filters terminating in midserics and the other in mid-shunt.

6. In a QQ-repeater circuithaving an am plifier in each path, a filter unit in the output circuit of the amplifier in one path, a second filter unit in the input circuit of the amplifier in the other path, the impedanceii'requency charactedstic ot the one unit being proportional to the reciprocal of that of the other.

7. In a QQ-repeater circuit having an amplifier in each path thereof, a filter unit included in the output circuit of the amplifier in one path. and another filter unit included in the input circuit of the amplifier in the other path, the impedance looking into saidfirst mentioned filter unit being greater than the internal impedance of the ampli fier. and the impedance-trequency curve of the other unit being proportional to the reciprocal of that of said first unit.

8. In QQ-repeatcr circuit having an amplifier in each path thereof, a filter unit in the output circuit of one amplifier and another filter unit in the input circuit of the other amplifier, said filter units being so related to each other that series impedanccs in the one will correspond to bridged admittances in the other.

9. In a QQ-repeater circuit having an amplifier in each path thereof, a filter unit in the output circuit of the amplifier of one path and another filter unit in the input circuit of the amplifier of the other path,

each of said units comprising series and shunt impedance elements, one of which is an inductance and the other of which is a capacity, the elements of the two filter units being so related to each other that the series inductance of the one corresponds to a bridged capacity of the other.

10, In a QQ-repeater circuit having an amplifier in each path thereof, a filter unit in the output circuit of the amplifier of one path and another filter unit in the input circuit of the amplifier of the other path, each of said units comprising series and shunt impedance elements, one of which is an inductance and the other of which is a capacity, the elements of the two filter units being so related to each other that the series inductance of the one corresponds to a bridged capacity of the other, and a series capacity of the one corresponds to a shunt inductance of the other.

11. In a QQ-repeater circuit having an amplifier in each path thereof, a filter section in the output circuit of the amplifier of one path and another filter section in the input circuit of the amplifier of the other path, each of said filter sections comprising series and shunt impedance elements, and one of said filter sections terminating in mid-shunt and the other section terminating in midseries.

12. In a QQ-repeater circuit having an amplifier in each path thereof, a filter section in the output circuit of the amplifier of one path and another filter section in the input circuit of the amplifier of the other path, each of said filter sections comprising series and shunt impedance elements, one of which is an inductance and the other a capacity, the elements of the two filter sections being so related to each other that a series inductance in one corresponds to a bridged capacity in the other and a series capacity in one corresponds to a shunt inductance in the other, one of said sections terminating in mid-series and the other in mid-shunt.

13. In a signaling system, a transmission circuit having branches, filter units in each of said branches, the impedance frequency curve of one of said filter units being proportional to the reciprocal of that of the other.

14. In a signaling system, a transmission circuit having branches, filter units in each of said branches, said filter units comprising series and shunt elements, the elements of the two units being so related to each other that for each unit a series impedance in one will correspond to a bridged admittance in the other.

15. In a signaling system, a transmission circuit having branches, filter units in each of said branches, each of said units comprising series and shunt impedances, one of negligible attenuation a band of frequencies while attenuating frequencies lying outside of the band, a connection between said filter and said circuit, said filter comprising complementary units each transmitting the same range of frequencies, and the impedance frequency curve of the one unit being proportional to the reciprocal of that of the other, so that the impedance of the combination will be substantially constant at all frequencies either within or without the band of free transmission.

18. In a signaling system, a transmission circuit, a band filter for transmitting with negligible attenuation a band of frequencies while attenuating frequencies lyingoutside of the band, a connection between said filter and said circuit, said filter comprising complementary units each transmitting the same range of frequencies, and each unit comprising series and shunt elements so related to each other that for each unit a series impedance inone will correspond to a bridged admittance in the other whereby the impedance of the combination will be substantially constant at all'frequencies either within or without the range of free transmission.

19. In a'signaling system, a transmission circuit, a band filter for transmittin with negligible attenuation a band of frequencies while attenuating frequencies lying outside of the band, a connection between said filter and said circuit, said filter comprising complementary units each transmitting the same range of frequencies, each of said units compr sing series and shunt impedances, one of which is an inductance and the other of which is a capacity, the elements of the two units being so related to each other that a series coil in the one corresponds to a bridged condenser in the other and a series condenser of one corresponds to a shunt coil of the other whereby the impedance of the combination will be substantially constant at all frequencies either within or without the range of free transmission.

20. In a signaling system, a transmission circuit, a band filter for transmitting with negligible attenuation aband of frequencies while attenuating frequencies lying outside of the band a connection between said filter and said circuit, said filter comprising complementary units each transmitting the same range of frequenc es, one of Said units terminating in midshunt and the other unit terminating in inidseries whereby the i111- pedance of the combination will be substantially constant at all frequencies either with in or Without the range of free transmission.

In testimony whereof I have signed my 10 name to this specification this 21st day of August, 1924.

HARRY NYQUIST. 

